Electromagnetic radiation image displaying panel

ABSTRACT

An image converting panel for displaying a pattern of short wave-length electromagnetic radiations, such as X-rays onto the image converting panel. The panel has a transparent substrate having at least the following layers thereon in the order from the bottom up; an electroluminescent layer having a dielectric constant of 7 to 40 and a thickness of d1; a reflective layer having a dielectric constant of 10 to 200 and a thickness of d2; an opaque layer having a specific resistivity of 105 to 1010, Omega -cm and a thickness of d3; a photoconductive layer having a linear relation of dark current to AC electric field up to at least 800 V/mm and a thickness of d4; an electromagnetic radiation permeable electrode; and a covering layer having a high resistance to humidity. The dimension d2 is equal to 0.1 to 0.3 d1; d3 is equal to 0.1 to 0.3 d1; and d4 is equal to 3 to 10 d1.

[ 51 Feb. 6, 1973 6 Primary ExaminerJames W. Lawrence IMAGE DISPLAYING PANEL Assistant ExaminerDavis L. Willis Inventors: Nobumasa Ohoshima, Osaka-fu; A't0mey wenderoth Lmd & Ponack Kinya Himeno, Nara-ken; Norihiro 57 ABSTRA T Tani, Osaka-fu,all of Japan l 1 C a An image converting panel for displaying a pattern of Asslgnee: Matsushlta Elecmc Industnal short wave-length electromagnetic radiations, such as anti-. 953?! lf X-rays onto the image converting panel. The panel has t 97 a transparent substrate having at least the following layers thereon in the order from the bottom up; an PP N063 77,406 electroluminescent layer having a dielectric constant of 7 to 40 and a thickness of d a reflective layer havu.s. Cl....................................250/80, 250/71 R' ing a dielectric constant of 10 to 200 and a thickness 51 Int. 1/62 of z an Opaque layer having a Specific resistivity of "250! R, 80 10 to 10'", Q-cm and a thickness of d a photoconductive layer having a linear relation of dark current References Cited to AC electric field up to at least 800 V/mm and a thickness of d.,; an electromagnetic radiation permea- UNITED STATES'PATENTS ble electrode; and a covering layer having a high re- 1 v sistance to humidity. The dimension d is equal to 0.1 to 0.3 d d; is equal to 0.1to 0.3 d and d is equal to I I 3 to 10d].

12 Claims, 5 Drawing Figures United States Patent Ohoshima et al.

[54] ELECTROMAGNETIC RADIATION 22i Filed:

[58] Field of Search...........................

PATENTED FEB 6 197a SHEET 10F 2 FIG] NOBUMASA OHOSHIMA, KINYA HIMENO and NORIHIRO TANI,

1N VENTOK 10 X-RAY RADIATION mr/ mm.

2 BY 'Zm/ A'ITORNEYS PATENTEDFEB 6|973 3,715,589

SHEET 2 OF 2 Tr? Ld l 610- (1) 4 1 [I I: [D G: 1; U1 U) z Ii d =6O MICRONS Q A I I I I I Q 2 4 6 8 IO 12 d4/d a RATIO OF THE THICKNESS OF THE PHOTOCONDUCTIVE LAYER 1 d TO ME ELECTROLUMIN QE ESCENT LAYER d TI FIG. 3 z K Oi D U J O 3, u? lOOO- NOBUMASA OHOSHIMA, KINYA HIMENO and NORIHIRO TANI,

500 1 l INVENTORSI I00 80 6O 40 0 case C015 0 2o so I00 WEIGHT, PERCENT HI 5 I 15d?! ATTORNEYS ELECTROMAGNETIC RADIATION IMAGE DISPLAYING PANEL This invention relates to an image panel for converting a pattern of radiations into a visible image by irradiating the panel with the radiations. The image converting panel is formed of two principal integrated layers, an electroluminescent layer and a photoconductive layer.

By radiations are meant such short waveelectromagnetic radiations as X-rays, 'y-rays and rays from a cathode tube. The following description is of a panel especially suited for use with X-rays, but the terms which refer particularly to X-rays should be understood as also applying to the other types of radiations.

An X-ray image has heretofore been converted into a visible image on a fluoroscopic screen including a fluorescent material such ascalcium tungstate. This method is not entirely satisfactory because of lack of brightness and contrast in the converted visible image. These inferiorities result in the vague images. A clinical X-ray examination requires a clearer visible converted X-ray image.

Much effort has been directed to providing an image converting panel which overcomes various deficiencies such as a poor brightness, an easy breakdown due to high voltage, impaired resolution of the image, and poor quality of the image, and which panel is capable of converting an X-ray image input to a visible image which is clearer, brighter and has a higher contrast than that of a conventional image intensifier system.

An object of this invention is to provide an X-ray image displaying panel for converting an input X-ray image to a visible image having satisfactory brightness,

sensitivity and range of input X-ray does rates at which the panel can operate satisfactorily, and to provide a method of converting an X-ray image to a visible image by using such a panel.

A further object of this invention is to provide an X- ray image displaying panel for converting an X-ray image to a visible image having highclarity and resolution.

These objects are achieved by providing a pane which has a transparent substrate having at least the following layers thereon in the order from the bottom up: an electroluminescent layer having a dielectric constant of 7 to 40 and a thickness of d,; a reflective layer having a dielectric constant of 10 to 200 and a thickness of d an opaque layer having a volume resistivity of 10 to IO Q-cm and a thickness of d;.; a photoconductive layer'having a linear relation of dark current to AC electric field up to at least 800 V/mm and a thickness of d an electromagnetic radiation permeable electrode; and a covering layer having a high-resistance tohumidity. The dimension d is equal -to 0.1 to 0.3 d,; d is equal to 0.1 to 0.3 d and d is equal to 3 to d,. When an X-ray image is irradiated on such a panel it is converted to a visible image.

These and other'features of this invention will be apparent from the following detailed description taken together with accompanying drawings wherein:

FIG. 1 is a cross sectional view of an image converting panel in accordance with this invention;

FIG. 2 is a graph illustrating the relation between the intensity of X-ray input and light output of the image converting panel;

FIG. 3 is a graph illustrating the relation between the light output and the ratio of the thickness of the photoconductive layer to the thickness of the electroluminescent layer of the image converting panel;

FIG. 4 is a graph illustrating the relation between the dark current and the AC electric field of photoconductive materials a, b, c, d, having various kinds of a linear relation to the voltage; and v FIG. 5 is a graph illustrating the relation between the electric field necessary for keeping the linear relation of the dark current and the quantity of CdS to CdSe in the photoconductive layer.

The solid state image converting panel according to this invention will be explained with reference to FIG. 1 of the drawings.

An image converting panel according to the present invention comprises a transparent substrate 1 having the following layers integrated thereon in order from the bottom to the top: a transparent electrode 2; an electroluminescent layer 3; a reflective layer 4; an opaque layer 5; a photoconductive layer 6; an X-ray permeable electrode 7; and a covering layer 8 having high resistance to humidity.

The thickness of these layers should be in the following relation:

d 25 to 80 microns d 0.1 a to 0.3 d

d 0.1 d to 0.3 d and d 3 d, to 10 d where d is the thickness of the electroluminescent layer d is the thickness of the reflective layer d;, is the thickness of the opaque layer d, is the thickness of the photoconductive layer.

Further, said photoconductive layer 6 should preferably have a linear relation between the dark current and the AC voltage up to at least an AC electric field of 800 V/mm. The electric field below which the linear relation is maintained will hereinafter be called the critical electric field. An AC voltage from a voltage source 11 is supplied across said X-ray permeable electrode 7 and said transparent electrode 2 through lead wires 9 and 10.

The novel image converting panel can be prepared by painting techniques, such as spray and screen methods which are well known. The transparent electrode 2 can be a tin oxide film chemically deposited on the transparent substrate 1. The tin oxide film can be covered by an electroluminescent paint to form the electroluminescent layer 3. The paint essentially consists of electroluminescent powder such as activated ZnS and a binder such as urea resin in a solvent such as xylol or butanol. The operable thickness of said electroluminescent layer 3 is 25 to microns.

The reflective layer 4 is prepared by applying, on said electroluminescent layer 3, a paint comprising barium titanate powder having particle size of from 0.5 to 10 microns and a binder such as urea resin in a solvent such as xylol or butanol.

A paint comprising carbon black powder and a binder such as epoxy resin in a solvent such as butanol and methylethyl ketone is applied to said reflective layer 4 for forming said opaque layer 5. Said photoconductive layer 6 can be prepared by using a photoconductive powder such as CdS or CdSe, a mixture thereof or a solid solution thereof and a binder such as epoxy resin in a solvent such as butanol and methlethyl ketone. Said photoconductive layer 6 can be applied in a thickness of 75 to 800 microns by, for example, a squeeze method.

The X-ray permeable electrode 7 is prepared by vacuum-evaporating a metal such as aluminum or indium on said photoconductive layer 6 and one end of said electrode 7 is connected to a copper electrode for electrical connection to a lead wire 9.

The covering layer 8 is prepared by covering adhesive material such as silicon rubber or silicon resin.

An explanation of how X-ray images projected on the image converting panel are converted will be given with reference to FIG. 1.

An X-ray input L, passing through the covering layer 8 and the X-ray permeable electrode 7 produces an impedance vpattern in the photoconductive layer 6. The more intense radiation results in lower impedance. When the AC voltage V, is applied across the X-ray permeable electrode 7 and the transparent electrode 2,

an electric current passes through the photoconductive layer 6, the opaque layer and reflective layer 4 and reaches the electroluminescent-layer 3.

The portions of the pattern having a low impedance permit a high electric current to flow into electroluminescent layer 3 and vice versa. Therefore, X-ray patterns projected on the photoconductive layer 6 can be converted, on the electroluminescent layer 3, into intensifled visible images.

The opaque layer 5 prevents the photoconductive layer 6 from being influenced by the images produced on the electroluminescent layer 3. The dielectric breakdown voltage of said electroluminescent layer 3 is improved by the provision of thereflective layer 4.

The images produced on the electroluminescent layer 3 vary in brightness with the amount and frequency of the applied AC voltage V,.

Referring again to FIG. 1, an AC voltage V, is applied across said lead wires 9 and '10. When an X-ray input L, having an intensity of 10 to 10 mr/min is projected on said photoconductive layer 6 through the covering layer 8 and the X-ray permeable electrode 7,

said electroluminescent layer 3 has a converted visible 7 image L, on the surface thereof. The light output L is intensified when an AC voltage V, of 200 to l,200 V at a'frequency of 60 Hz to 10 kHz is applied across said lead wires 9 and 10.

Reproduced visible images which have satisfactory brightness, contrast, resolution and clarity can be provided by-adjusting the X-ray intensity in accordance with the kind and the thickness of materials to be inspected..The thickness relations described above are very'important for providing improved brightness and the latitude of the visible image reproduced on the X- ray image displaying panel. As shown in FIG. 3, a ratio d,/d, in a range of 3 to 10 results in a high brightness of the image on the image converting panel. When the ratio d,/d, is higher than 10 for d, =80 microns, the photoconductive layer 6 has a thickness greater than 800 microns. It is difficult to dry and cure such a thick layer uniformly. An uneven-photoconductive layer 6 results and is apt to reproduce uneven images. When the ratio d, /d, is lower than 3 for d, =25 microns, the photoconductive layer 6 has a thickness less than 75 microns. In such a thin layer, the photoconductor particles are not distributed uniformly because of the relatively large size of the photoconductor particles.

The contrast of images can be adjusted freely by changing the ratio of the thickness of the photoconductive layer 6 to the thickness of the electroluminescent layer 3 within the thickness relations described above.

It is preferable that they electroluminescent layer 3 have a dielectric constant of 7 to 40. A dielectric constant less than 7 makes the impedance of the electroluminescent layer 3 higher. Therefore, the ratio of the impedance of the electroluminescent layer 3 to that of the photoconductive layer also becomes higher. As a result, the reproduced images have a high brightness, but has inferior clarity. When the dielectric constant of the electroluminescent layer 3 is higher than 40, the impedance of the electroluminescent layer 3 becomes too low. The ratio of the impedance of the electroluminescent layer 3 to that of the photoconductive layer 6 becomes lower. As a result, the reproduced images have superior background brightness, contrast and clarity, but have inferior maximum brightness.

The reflective layer 4 preferably has a dielectricconstant of 10 to 200. A reflective layer 4 having a dielectric constant lower than 10 has a high impedance, even when it is very thin. Therefore, the voltage drop in said layer 4 becomes fairly large and the voltage applied to the electroluminescent layer 3 is lower. When the dielectric constant is higher than 200, the impedance of the reflective layer 4 decreases and the electric current in the lateral direction near the surface of the reflective layer 4 increases. As a result, the reproduced image is not clear.

. The opaque layer 5 preferably has a specific resistivity of 10 to 10? .Q-cm. When the specific resistivity of said opaque layer 5 is higher than the dark specific resistivity of the photoconductive layer 6, it is difficult for the electric current to flow through the photoconductive layer 6. Therefore, the reproduced images do not have satisfatory maximum brightness and contrast. An opaque layer 5 having a specific resistivity less than 10" Q-cm permits an electric current to flow easily through the photoconductive layer 6. The impedance of the photoconductive layer 6 under X-ray irradiation decreases. Therefore, the reproduced images have greatly improved in maximum brightness as well as contrast.

A lower specific resistivity of said opaque layer 5 results in a lower impedance in the lateral direction in said opaque layer 5; this impairs the clarity of the images. The clarity of the images depends also upon the thickness of the opaque layer 5. The lack of clarity of the images can be eliminated by decreasing the thickness of the opaque layer 5.

In order to improve the quality and resolution of the reproduced images, the X-ray permeable electrode 7 is made of a radiation permeable metal, such as indium or aluminum, covering the whole surface of the photoconductive layer 6 and can be prepared by a vacuum deposition method. This makes it possible to manufacture a large-sized panel and to improve the production yield of panels having high stability and reliability.

The reflective layer 4 and the opaque layer 5 are preferably as thin as possible, within the relations described above, in order to reduce the voltage applied across the image converting panel.

The opaque layer 5 should be sufficiently thick to prevent the feed back of light from the electroluminescent layer 3 to the photoconductive layer 6. The reflective layer 4 is provided to give a satisfactory breakdown voltage of the panels. The thickness of each layer should be about microns.

The image reproducing panel according to the present invention can omit the current diffusing layer which is necessary for a conventional image reproducingpanel according to the prior art, for example, as disclosed in Proceedings of the IRE, 43, No.3 (1955), pp. 1888-1897. The elimination of the current diffusing layer results in a thinner panel which works well at a low applied voltage.

It is necessary for the resultant panel to be protected from humidity and corrosive gases. To this end, a covering layer 8 is formed on the X-ray permeable electrode 7. A suitable material for the covering layer 8 is, for example, silicon rubber, silicon resin or wax which allows X-rays to pass therethrough. Care should be taken that the binder chosen does not reduce the sensitivity of the photoconductive layer 6, because the photoconductive layer 6 is badly influenced by the binder in the covering layer 8 and the shrinkage thereof during hardening. For example, when resins such as epoxy and urea resin are used as a covering material,

the image converting panel without the covering layer 8 is kept in an atmosphere having a relative humidity of 100% for several hours, the photosensitivity of said panel drops greatly. Further, the impairment is made worse when such a panel is operated in a high humidity atmosphere.

The covering layer 8 must therefore be made of a material having a suitable plasticity and elasticity after hardening andhaving the high resistance to humidity, such as silicon resin, silicon rubber and waxes.

A conventional image converting panel uses conventional glass or color glass as a transparent substrate 1. But these glass plates can not protect sufficiently against the X-ray radiation escaping from the electroluminescent layer 3. An operator must observe the reproduced image through a transparent lead glass plate placed in front of the transparent substrate 1. Such a disadvantage can be avoided by using, as a transparent substrate 1, a glass which includes lead in an amount such that the glass is equivalent to lead 1 to 10 mm thick. Moreover, the use of such a glass can decrease the reflection and the refraction ofimages.

Referring to FIG. 1, one specific practical embodiment of the present invention has the following layers on the transparent substrate 1 in the order from the bottom up; the transparent electrode 2 consisting of tin oxide, the electroluminescent layer 3 (60 microns) consisting of powdered activated ZnS and a cellulose binder, the reflective layer 4 (10 microns) consisting of barium titanate powder and a urea resin binder, the opaque layer 5 (10 microns) consisting of carbon powder and an epoxy resin binder, the photoconductive layer 6 (320 microns) consisting of photoconductive powder of activated CdS and an epoxy resin binder, the X-ray permeable electrode 7 consisting of a uniformly evaporated aluminum film, and the covering layer 8 consisting of silicon resin. The photoconductive layer 6 has a linear relation of dark current to voltage up to 1,900 V/mm.

The thickness d of the reflective layer 4 and d of the opaque layer 5 is equal to 0.16 the thickness d of the electroluminescent layer 2, and the thickness of d, of the photoconductive layer 6 is 5.3 d,.

A curve C of FIG. 2, shows the relation between the brightness and the X-ray input intensity when the panel is operated at an AC voltage of 500 V at 1 kHz.

Curves d, a and b of FIG. 2 showthe same relation for panels using a conventional fluoroscopic screen, a grooved electrode type and parallel fine wire type grid electrodes, respectively, for the image intensifier. The fluoroscopic screen is made by Dainippon Toryo Co. in Japan and is composed of a fluorescent powder of calcium tungstate and a binder of nitrocellulose. It has a thickness of about 200 microns.

It is clear that the image converting panel according to this invention has greatly improved brightness. The image reproduced on said panel has a contrast of 1 to 1.5 and a range of X-ray does input of two figures. Further, it has a high quality and a high resolution, on the order of 2 to 4 line pairs/mm.

, FIG. 4 shows that various photoconductors ranging from pure CdSe through various mixtures thereof with CdS to pure CdS have various relations of dark current to electric field. These photoconductors also have various critical electric fields as shown in Table 1, in which Ed designates the critical voltage; Vapp is the AC voltage at 1 kHz applicable to the resultant panel without producing flickers on the panel; Ed is the brightness of the resultant panel at dark; B is the brightness of the resultant panel when illuminated by an X-ray; and R is the ratio, B lB A higher E results in a lower Ed and a high Vapp results in a higher 8,. Therefore, a higher R, i.e. a higher contrast of the reproduced image, is obtained by a photoconductor having a higher 13,. I

The panel according to the present invention can reproduce a visible image clear and bright enough to be seen in ordinary room light.

Usually, photoconductive materials for an image converting panel are composed of finely powdered CdS or CdSe activated by Cu or Ag and coactivated by C1 and Al. These powders are heated in a non-oxidizing gas such as nitrogen or argon at ahigh temperature of 500 to 800 C. However, both photoconductors have merits and demerits, respectively, and a photoconductor having a satisfactory performance has not been obtained heretofore. An image converting panel using using CdSe photoconductive powder has a satisfactory response characteristic, but the other characteristics are inferior.

Moreover the use of CdS or CdSe alone does not satisfy all the requirements for brightness, sensitivity and quality of the reproduced image as well as the response characteristics. A photoconductive layer using only CdS powder has a linear relation of dark current to voltage up to a critical electric field higher than 2,000 V/mm. A photoconductive layer using only CdSe powder has a linear relation of dark current up to a critical electric field lower than 1,000 V/mm. Also in a photoconductive layer 6 having only CdSe powder, the dark current increasesabruptly at a low applied voltage and the impedance decreases abruptly. The background brightnessof the reproduced image increases greatly; the contrast and clarity of the reproduced image becomes poor. Further, a flicker appears due to a localizedbreakdown in the photoconductive layer 6 and impairs the quality of images. Generally, when a linear relation of dark current to voltage is present up to the higher critical electric field, the brightness and quality of reproduced images are better. However, the photoconductive materials having an excellent linear relation of the dark current to voltage do not have a high sensitivity or a high response characteristics.

In order to provide a reproduced image having high sensitivity and high brightness on said panel in a lighted room, the photoconductive layer 6 must be free from breakdown and must not flicker even when supplied with a high AC voltage. A good result can be obtained by using a photoconductive layer having a linear relation of the dark current to voltage up to more than 800 V/mm, because the photoconductive layer having a linear relation of the dark current to voltage up to an electric field less than 800 V/mm can not be supplied with a high voltage due to flickering, and the brightness of the images is poor. However, the background brightness of the images does not decrease greatly. The reproduced image has poor contrast and poor clarity and is not usable for practical purposes.

, The use of photoconductive material having a linear relation of the dark current to'voltage up to more than 800 V/mm does not produce flickers and does not increase the background brightness even when the high voltage necessary for satisfactory brightness is applied to said panel across the lead wires. Therefore, the reproduced images have a high brightness and high clarity as well as high contrast.

In the panel described above, the photoconductive layer 6-is of a CdS type photoconductive powder. However, photoconductive material such as activated CdSe and mixtures of CdS and CdSe can be used to achieve different features in response to different requirements. An image converting panel using the photoconductive materials corresponding to the curves b, c and d of FIG. 4 or Table 1 can be supplied with a high AC voltage of 430 to 620 V at 1 kHz. The images reproduced on these panels are clear and bright and have a brightness of 5 to ft-L, a high quality and a high contrast without flickers. The panel is free from the localized discharge and breakdown and has a long life.

The image converting panel using the photoconductive material corresponding to the curve a of FIG. 4 can not be supplied with a high AC voltage because flickers will be produced. The reproduced image on this image converting panel has a brightness less than 4 ft-L and a high background brightness. The contrast is much poorer than for an image converting panel using CdS or mixtures of CdS and CdSe for the photoconductive layer 6. In addition, flickers arise .even at the low applied AC voltage.

The use of activated CdSe also for the photoconductive layer 6 is thus inferior to CdS alone or mixtures of CdS and CdSe in the linear relation of dark current to voltage, but is superior in the response time to the use of activated CdS alone.'

In view of the balance of these properties, the photoconductive layer preferably includes a photoconductor having a composition consisting essentially of 40 to wt. of CdSe and 20 t0 60 wt. of CdS. A higher wt.% of CdS results in a higher critical voltage below which said linear relation isheld as shown in FIG. 5. A photoconductor having activated CdS in an amount less than 20 wt% has a lower E and a photoconductor having activated CdS in an amount greater than 60 wt. has impaired response time.

As described above, a mixture of photoconductors CdS and CdSe is used to achieve the intermediate features of the CdS or CdS type photoconductor. However, a percent CdS type photoconductor is better for a still image and a 100 percent CdSe type photoconductor is more suitable for a moving image.

The panel according to the invention is equally useful for -y-rays, and when placed in a vacuum, for rays from a cathode tube.

We claim:

1. An electromagnetic radiation image displaying apparatus comprising an energized image converting panel which comprises a transparent substrate having at least the following layers thereon in the order from the bottom up:

a transparent electrode;

an electroluminescent layer having a thickness d of 25 to 80 microns; a

a reflective layer having a thickness of d an opaque layer having a thickness of d a photoconductive layer having a thickness of d,;

an electromagnetic radiation permeable electrode;

and

a covering layer wherein:

d is equal to 0.1 d to 0.3 d,;

d is equal to 01 d to 0.3 d and d. is equal to 3 d to 10 d,, and means coupled to said panel for energizing said panel, whereby when said energized image converting panel is exposed to an electromagnetic radiation image, the image is converted into a visible image on said energized image converting panel.

2. An image displaying apparatus as claimed in claim 1 wherein said energizing means is means for applying across said transparent electrode and said electromagnetic radiation permeable electrode a voltage of 200 to 1,200 volts at frequency of 60 Hz to 10 kHz, whereby the panel can convert to a visible image a radiation pattern having an intensity of l to mr/min.

3. An electromagnetic radiation image converting panel comprising a transparent substrate having at least the following layers thereon in the order from the bottom up:

a transparent electrode;

an electroluminescent layer having a thickness of 25 to 80 microns d,;

a reflective layer having a thickness of d a opaque layer having a thickness of d a photoconductive layer having a thickness of 1 an electromagnetic radiation permeable electrode;

and

a convering layer, wherein;

d is equal to 0.1 d to 0.3 d

d is equal to 0.1 d, to 0.3 d,; and

[1 is equal to 3 d, to 10 d 4. An image converting panel as claimed in claim 3 wherein said electroluminescent layer is zinc sulfide based electroluminescent material in a binder, said reflective layer is barium titanate in a binder and has a thickness of 2.5 to 24 microns, said opaque layer is carbon black in a binder and has a thickness of 2.5 to 24 microns, and said photoconductive layer is a material selected from the group consisting of cadmium sulfide based photoconductor, cadmium selenide based photoconductor and mixed cadmium sulfied and cadmium selenide based photoconductor and has a thickness of 75 to 800 microns.

S. An image converting panel as claimed in claim 4, wherein said photoconductive layer is a photoconductor composition consisting essentially of 40 to wt. of cadmium selenide and 20 to 60 wt. of cadmium sulfide.

6. An image converting panel as claimed in claim 4, wherein said electroluminescent layer has a dielectric constant of 7 to 40.

7. An image converting panel as claimed in claim 4, wherein said reflective layer has a dielectric constant of 10 to 200.

8. An image converting panel as claimed in claim 4, wherein said opaque layer has a specific resitivity of 10 to l0 Q-cm.

-9. An image converting panel as claimed in claim 3, wherein said photoconductive layer has a linear relation of dark current to voltage up to at least 800 V/mm.

10. An image converting panel as claimed in claim 3, wherein said electromagnetic radiation permeable electrode covers the whole of said photoconductive layer and consists of a vacuum-evaporated metal film, said metal being one member selected from the group consisting of aluminum and indium.

11. An image converting panel as claimed in claim 10, wherein said covering layer over said metal evaporated film is resin having a curing shrinkage from 0 to 4 percent.

12. An image converting panel as claimed in claim 3, wherein said transparent substrate is one member selected from the group consisting of conventional glass, color glass, and a lead glass including lead in an amount such that the glass is equivalent to lead 1 to 10 mm thick. 

1. An electromagnetic radiation image displaying apparatus comprising an energized image converting panel which comprises a transparent substrate having at least the following layers thereon in the order from the bottom up: a transparent electrode; an electroluminescent layer having a thickness d1 of 25 to 80 microns; a reflective layer having a thickness of d2; an opaque layer having a thickness of d3; a photoconductive layer having a thickness of d4; an electromagnetic radiation permeable electrode; and a covering layer wherein: d2 is equal to 0.1 d1 to 0.3 d1; d3 is equal to 0.1 d1 to 0.3 d1; and d4 is equal to 3 d1 to 10 d1, and means coupled to said panel for energizing said panel, whereby when said energized image converting panel is exposed to an electromagnetic radiation image, the image is converted into a visible image on said energized image converting panel.
 2. An image displaying apparatus as claimed in claim 1 wherein said energizing means is means for applying across said transparent electrode and said electromagnetic radiation permeable electrode a voltage of 200 to 1,200 volts at frequency of 60 Hz to 10 kHz, whereby the panel can convert to a visible image a radiation pattern having an intensity of 100 to 104 mr/min.
 3. An electromagnetic radiation image converting panel comprising a transparent substrate having at least the following layers thereon in the order from the bottom up: a transparent electrode; an electroluminescent layer having a thickness of 25 to 80 microns d1; a reflective layer having a thickness of d2; a opaque layer having a thickness of d3; a photoconductive layer having a thickness of d4; an electromagnetic radiation permeable electrode; and a convering layer, wherein; d2 is equal to 0.1 d1 to 0.3 d1; d3 is equal to 0.1 d1 to 0.3 d1; and d4 is equal to 3 d1 to 10 d1.
 4. An image converting panel as claimed in claim 3 wherein said electroluminescent layer is zinc sulfide based electroluminescent material in a binder, said reflective layer is barium titanate in a binder and has a thickness of 2.5 to 24 microns, said opaque layer is carbon black in a binder and has a thickness of 2.5 to 24 microns, and said photoconductive layer is a material selected from the group consisting of cadmium sulfide based photoconductor, cadmium selenide based photoconductor and mixed cadmium sulfied and cadmium selenide based photoconductor and has a thickness of 75 to 800 microns.
 5. An image converting panel as claimed in claim 4, wherein said photoconductive layer is a photoconductor composition consisting essentially of 40 to 80 wt. % of cadmium selenide and 20 to 60 wt. % of cadmium sulfide.
 6. An image converting panel as claimed in claim 4, wherein said electroluminescent layer has a dielectric constant of 7 to
 40. 7. An image converting panel as claimed in claim 4, wherein said reflective layer has a dielectric constant of 10 t0
 200. 8. An image converting panel as claimed in claim 4, wherein said opaque layer has a specific resitivity of 105 to 1010 Omega -cm.
 9. An image converting panel as claimed in claim 3, wherein said photoconductive layer has a linear relation of dark current to voltage up to at least 800 V/mm.
 10. An image converting panel as clAimed in claim 3, wherein said electromagnetic radiation permeable electrode covers the whole of said photoconductive layer and consists of a vacuum-evaporated metal film, said metal being one member selected from the group consisting of aluminum and indium.
 11. An image converting panel as claimed in claim 10, wherein said covering layer over said metal evaporated film is resin having a curing shrinkage from 0 to 4 percent. 